Heat and its importance in citrus

Sep 28, 2009

Ventura County UCCE Farm Advisor Ben Faber shares with us some of his citrus tree knowledge.

Heat affects different types and varieties of citrus differently. Heat determines when fruit ripens and how sweet it will be.  Grapefruit has one of the highest heat requirements of all citrus.  Grown along the coast it will be sour, but in the Central Valley it can be decidedly sweet.  A Pixie mandarin along the coast will be 6-8 weeks later in ripening than the Valley and will hang on the tree much longer.  Acid fruits like lemon and ‘Bearss’ lime have low heat requirements and are well adapted to the coast.  The everblooming characteristics of lemons and limes are accentuated along the coast where there may be continuous cropping with lemon blooms year round.

High temperatures can have a negative effect on citrus.  Coastal citrus may suddenly drop fruit when temperatures swing from the cool 60’s to the 90’s as often happens with Santa Ana conditions.  Sudden warm weather can cause fruit to split, induce flower and leaf drop, and cause sudden burn to both the fruit and tree.  These problems are compounded by dry soil moisture and problems can be reduced if there is adequate moisture present during the heat wave.  In hot environments, some citrus like navels produce less fruit.